Romero recovered after making a double-bogey on the par-three eighth hole to birdie six of the last nine holes and reach the halfway stage as the outright leader at 14-under.
"What's helped me is going back to my old putter. It's really been great for me," Romero told reporters.
"I'm also striking the ball well. So finally all three things have come together, putting well, hitting my irons well, driving well."
Scott Brown of the United States climbed 12 places and into sole possession of second place after firing a 63 that put him at 13-under for the tournament after a round that included eight birdies and an eagle at the par-four seventh.
"I got off to just a very normal start," said Brown.
"(I) birdied both par-fives on the front, was hitting it good and then I holed a shot out on seven from the fairway with a seven-iron."
Peter Uihlein and fellow American Steve LeBrun both signed for 65s to end the day at 12-under, a stroke clear of Argentina's Fabian Gomez, whose 64 took him to 11-under.
Two-time Major winner Angel Cabrera was among a group of nine players, including defending champion George McNeill and joint overnight leader Cameron Percy, at nine-under.